From Yahoo answers
No intelligence is some thing of a grey area, many people in MENSA for instance cant spell, and talk gibberish. Try going to there web site for yourself. The brain is a very complex organicism, there are few hard and fast rules that can define inelegance or a high IQ, in fact some people you might dismiss can have a very high IQ, while others in positions of authority can have an average intelligence, for instance look at the last few British Prime Ministers. A failed bus conductor for one.
Grammar / spelling are the ability to copy and repeat, that’s a memory question not one of inelegance, the more connection the brain makes, the more likely undesirable side effects are likely to crop up. Many of the most famous and intelligent people thought out history, have had problems with spelling / grammar / explaining themselfs. As they see things in a different way, Newton for instance cant have been the first person to have some thing fall on his head,
If your really interested you might want to take a course in non clinical psychology, or just view some of the papers on line. They can get a bit heavy, so a look at the MENSA web site might be all your looking for.